use python-keyring for password management

python keyring provides a interface for multiple password manager such
as OSXKeychain,KDEKWallet or GnomeKeyring.

http://pypi.python.org/pypi/keyring
added config option for using keyring module

thx to @tresni for suggestion
Merge branch 'error_correction' into new_master
Merge remote-tracking branch 'mzur/master' into new_master
Merge in customLocale changes
--cal now overrides list of calendars to work with, as documented
Merge support for reminder settings
Merge branch 'fix_time_display'
Merge branch 'error_correction'
Merge branch 'sanity_checks'